A 24-h infusion of 5FU and leucovorin will be administered to patients with elevated bilirubin or creatinine and the maximum tolerated dose of the combination will be established. Plasma levels of 5FU will be obtained for pharmacodynamic analysis and to study circadian variation of 5FU levels during 24 h infusion and to correlate them with dehydrogenase levels in peripheral blood lymphocytes.